Acute Shortness of Breath (<2-3 weeks) — Full Text

In both Greek & Medical-Speak, the word is “dyspnea” = difficult breathing.  We’ll stick with the English “Shortness Of Breath,” which gets abbreviated “SOB” all over the country (one reason some clinicians won’t let patients look at their charts).  Please note that our text may be somewhat long.  SOB is a concerning symptom, so completeness seemed important. Scrolling down identifies main sub-topics.  See also Acute SOB — Summary Approach for a clinician’s nutshell thought process.


This topic addresses the causes of “true” SOB.  The term “true” is my invention, not used by clinicians in general.  But I use it here, because some people who say they feel “short of breath” really have no problem getting enough oxygen. Reasons they say so include:

  • Nose is all stuffed up
  • A bad coughing spell
  • Stomach-acid reflux (GERD)
  • Frequent need to “sigh”
  • Anxiety, especially with hyperventilation or panic
  • Deconditioning

See our definition “True” Shortness of Breath, which also discusses a common Spanish mistranslation.

From now on, this topic addresses “true” SOB, meaning the body isn’t getting the oxygen it wants.  Causes have mainly to do with the lungs, heart, and the blood’s ability to circulate.


This is always our first step, even before diagnosis.  We determine the degree of seriousness by counting the heart & respiratory rates, & measuring how much oxygen blood is carrying: the “oxygen saturation” (O2 Sat).  A painless sensor is attached to finger or ear lobe; ≥95% saturation is fine, ≤90% is bad, 91%-94% uncertain. See link above for misleading situations.

However, the O2 Sat is just an approximation of how much oxygen is in the blood.  A seriously-SOB patient requires a “blood gas,” done in ER or hospital, which checks exact levels of oxygen & carbon dioxide, and measures the blood pH (acidity).  It can provide essential information about how bad things are.

To identify Life-Threatening SOB, all we need are our own eyes.  We worry if we note:

  • Pausing for breath every few words (respiratory rate ≥24 times per min.)
  • “Retractions”: skin sucks in with each breath at bottom of neck, above collarbones, between ribs
  • Oxygen saturation <90% (if pulse oximeter available)
  • Lips, fingers, face look blue call 911
  • Agitation, can’t think straight
  • Somnolence, just sleeps

See topic Shortness of Breath — Life-Threatening for an in-depth discussion.

ACUTE SHORTNESS OF BREATH (“SOB”)  (going on 2-3 weeks or less)

Anyone who says they feel “SOB” may not be allowed inside a building without a Covid Test. But some patients need to be seen no matter what; every office or clinic should have its own mechanism, maybe in a designated exam room, maybe calling an ambulance. If they’re having a Heart Attack, we don’t want them to wait 2-3 days (or more) for Covid results.

The following Table lists the possible causes of Shortness of Breath (SOB) that has begun rather recently, less than 2-3 weeks, often a matter of days or even hours. Almost always, their SOB isn’t felt at rest and only occurs with exertion, maybe just with simple walking if serious, although usually something a little more demanding.  Our discussion now assumes that there are NO signs of life-threatening lack of oxygen.

Causes of Acute (Recent-Onset) Shortness of Breath (SOB)


Myocardial Infarction (M.I.) xxx (heart attack)
Angina (coronary artery xxxdisease)
Heart Failure (HF)
Early Shock (e.g. Sepsis)

Pulmonary Embolism (PE)
Bronchospasm (from Viral xxBronchitis, Asthma, or COPD)
Uncommon Lung Conditions

Anaphylaxis (allergy)
Obstruction in Upper Airway  


Rare Causes

Virtually all of the above conditions, once having begun, will persist throughout the day, every day. They won’t occur one day, not the next, then recur. They won’t feel bad in the morning, disappear completely, then come back a little in the evening. The main exception is Angina, blockage of the heart’s coronary arteries that is felt in bursts (as opposed to a full-blown Heart Attack, when symptoms persist). These are described below. Asthma, also, may vary from week to week, month to month, etc.

That last bottom category “Rare Causes” doesn’t look so reassuring — “What if I’ve got one of them?!?”  Many can be seen by a chest x-ray.  Others, the patient will be sick enough so as to go or be sent to an ER.  But feel free to click the link for Rare Causes of SOB, so if you or your loved one [or even worst enemy] is suddenly dying without explanation, you can ask the ER docs, “Could it possibly be ____?”

On to the common causes of Acute (i.e. recent) “true” SOB, and how we clinicians approach them.  In many cases, our final diagnosis will be easily-manageable Bronchospasm, but our first consideration is always conditions which potentially could be most immediately lethal…

**  Heart Attack (Myocardial Infarction) (“M.I.”)  —  We think of heart attack going along with “chest pain,” but some patients mainly experience SOB.  The problem is, lots of people with M.I.’s are in denial.  “At the same time you feel short of breath, do you have any chest pain?”  “NO !!!!!”  So I vary the question:

  • “Do you have a little pressure?”  “…ache?”  “…heavy feeling?”  “…tightness?”
  • “…in your left shoulder?”  “…top of your belly?”  “…left upper arm?” “…left jaw?”

Sometimes it’s the dentist who makes the diagnosis, when a patient seeks care for a “toothache.”

If the patient does acknowledge some sort of pain along with the SOB, we ask what it feels like.  Heart pain feels dull, achy, heavy, pressing, squeezing.  It’s not stabbing, & certainly not “pleuritic” (made worse by deep breaths or coughing).

We also ask about other key symptoms suggestive of heart attack: “At the same time you feel short of breath, do you:

  • …get nausea, or vomit?”
  • …break out in a cold sweat on your forehead?”
  • …feel lightheaded or dizzy, like you might faint?”

The more of these that are positive, the more we think “heart.”

Heart attacks are caused by Coronary Artery Disease.  Any time a person with risk factors for Coronary Artery Disease seeks care for SOB, we automatically think “Maybe an M.I.?”  No risk factors, and the likelihood will be very low.  These risks are mainly:

  • Age: Men over 35; Women after menopause
  • High Blood Pressure (as a diagnosed illness)
  • Diabetes
  • Smoking
  • High Cholesterol
  • Same-day use of cocaine / methamphetamines

Physical exam is almost always completely normal in the midst of an M.I.  There may be signs of heart failure (see below), but typically not.  We might order an EKG for a person with risk factors & new SOB, but the EKG can be normal even during an M.I. 

If we have any thought that a patient might be having an M.I., we stop what we’re doing and call 911.  Just like the recording tells you to do every time you telephone any sort of health care facility.  See also our discussion of heart attacks under Diagnosing Coronary Artery Disease.

**  Angina  —  This is coronary artery disease, just like a heart attack, but hasn’t yet progressed to the point of causing irreversible death of any heart muscle.  People don’t die with Angina, but the danger is that a full-blown M.I. might occur at any moment.

Clinically, in terms of symptoms, the difference between Angina and an M.I. is that the SOB of Angina is short-lived and intermittent.  It doesn’t last longer than a few minutes (but always more than just seconds), and usually occurs or worsens with some sort of exertion.

We seek the same history as we would for a possible M.I.:

  • Risk Factors for Coronary Artery Disease
  • Chest pain (‘pressure,’ etc.) occurring along with the SOB
  • Other key symptoms occurring along with the SOB (see Heart Attack above)

If we think that SOB might be due to Angina, and a patient’s pattern seems “progressive,” we call it “Unstable Angina.”  This would be like they used to get SOB walking up 2 flights of stairs (or blocks, etc.), then just 1, and now the episodes of SOB occur with the least little exertion (or even at rest).  For Unstable Angina, we call 911.

For episodes of SOB that sound unchanged, i.e. like “Stable Angina,” we obtain an EKG and order stress testing for diagnosis.  In the meantime, we prescribe maximum treatment for coronary artery disease, just in case.  See Coronary Artery Disease (CAD), and also our discussion Diagnosing CAD.

**  Pulmonary Embolism (PE)  —  among the common causes of SOB, this may be the toughest diagnosis of all.  Among all potentially lethal conditions, it may be the one most frequently missed.

A blood clot, dislodged from a vein in the legs or pelvis, gets swept within the blood circulation, travels up to heart, & gets stuck in the lungs.  A large clot cuts off most of the blood supply & may be rapidly fatal.  A tiny one winds up in the lung periphery, but the danger is that a bigger clot may be looming from the original source. A clot in place where it formed is a “thrombus”, when it gets dislodged and travels downstream, it’s called an “embolus”.  “Embolism” refers to the disease.

PE is a very tricky disease.  Chest x-ray and EKG are usually normal.  And if abnormal, they can look like other conditions such as pneumonia or heart conditions.  The main error clinicians make is simply failure to “Think PE.”

When “thinking PE,” we need to focus on two key diagnostic parameters:

1.  Acute Onset:  Shortness of breath begins within seconds 46% of the time, within 2 minutes another 26%.  It makes sense — the clot in the leg is asymptomatic until it floats up, gets stuck in the lungs, then bingo, there’s SOB.

2.  Risk Factors:  The biggest one is clinical symptoms suggesting a clot in a leg vein.  The medical term is Deep Venous Thrombosis (DVT).  Symptoms may be:

  • pain, tenderness, or swelling by a femoral vein (inside area of upper thigh)
  • new swelling in just one foot, with no explanation (very rarely, an arm)

However, even though most people with a PE also have DVT, the clot in place is usually asymptomatic.  So we need to look at other significant risk factors for getting clots in general:

  • Immobilization for ≥3 days (e.g. long-legged cast)
  • Anesthesia within the past 4 weeks
  • Active cancer
  • Prior history of either DVT or PE.
  • Pregnancy, or under 3 months post-partum
  • HIV infection, though not usually listed, predisposes to blood clots. Covid-19 also.

Other concerning findings, not as common or as diagnostically strong, include:

  • Rapid heart rate (Tachycardia)
  • Rapid respiratory rate
  • Coughing up blood
  • Obese women with hypertension who smoke

A normal oxygen saturation measurement (“O2 Sat”) that doesn’t decrease with exertion speaks strongly against a PE.

ER’s have validated clinical scoring charts & questionnaires to assess the probability of PE.  A key criterion, just as strong & predictive as concurrent DVT symptoms, is, “does another diagnosis appear likely?”  Not “guessed,” but likely.  New-onset SOB is serious.  If there’s no obvious explanation, we need to think PE.

A brief word about tachycardia (rapid heart rate); medical lore often suggests that it’s the “most common sign.”  Maybe so for big clots, when compared to other findings on exam, but physical exam is usually not helpful.  Most patients with PEs have normal heart rates.  I’ve seen the diagnosis missed by clinicians who dismiss the possibility because, “he’s not tachycardic.”  Tachycardia is useful when found, but not for its absence.

Some “risks” we may read about aren’t so significant.  Estrogens, like in birth control pills, increase the relative risk 2- to 4-fold, but absolute risk remains very low (click link for an illuminating summary of risk interpretation).  And in terms of airplanes, a healthy traveler who flies 5,000 miles may have only a 3-in-a-million risk.  These risks are not factored into clinical scoring tools, because they’re way too low.  But they raise eyebrows among the public, & among health professionals, who in our own personal lives may relate more easily to plane flights & birth control than to cancer or leg casts.

So we send patients with new-onset SOB to an ER to rule-out a PE if:

  • Their SOB began very suddenly, & there’s no other explanation for them.
  • They have risk factors for PE, and there’s no other obvious diagnosis.

The ER will obtain a blood test for D-dimer, a molecule produced by blood clots (& by lots of other conditions).  A negative D-dimer means no clot; a positive just means we can’t rule out PE.  Then we generate a clinical probability score based on risk factors, history, & physical exam [e.g. JAMA 2006; 295:171], & decide if there’s enough likelihood to perform further testing, usually a lung CT scan.

Why not just do those tests anyway?  Partly to avoid radiation exposure, unlikely risks of the CT dye,  & expense.  But mostly because they’re not perfect; each gives a certain number of false-positives.  Then we’re stuck prescribing anticoagulants (“blood thinners,” with risk of hemorrhage) or ordering an invasive pulmonary angiogram to be sure (with slight risk of causing a PE, or death).  Read why to Never Order Tests if there’s Low-Probability of Disease.

By the way, bruises (black-and-blue marks, often from injuries) are clotted blood under the skin, but not within a vein.  So that kind of clot can’t float anywhere, & is no danger whatsoever.

** Covid-19 — We already said we’d get a Covid test for everyone with SOB. Well, 15% to 20% of the time the result may be false-negative. If the patient has other symptoms suggestive of Covid besides simply SOB, we examine the patient same-day with appropriate precautions, maintain isolation for another 2-3 days, and obtain a second test.

**  Heart Failure (HF)  —  The heart is a pump; there are various reasons why it may pump weakly.  But they all cause the same symptom: SOB.  If the weakness is slight, the SOB only occurs with significant exercise.  If very weak, the least little exertion is difficult.  Note that heart “failure” doesn’t mean the heart has stopped, just that it’s pumping weakly.

To diagnose HF (also called CHF, “congestive heart failure”), we ask about its other symptoms as well:

  • Edema (swelling, usually in the feet)
  • Orthopnea: have to sleep with lots of pillows, or sitting up
  • Waking up at night suddenly, short of breath

We also inquire about recent chest pain, that could have been a heart attack.  An M.I. is a common cause of subsequent, ongoing HF.

Physical exam is quite useful when it comes to HF.  When the heart doesn’t pump well enough, blood flow stagnates, & fluid leaks into the lungs & feet.  We can detect a number of key findings:

  • “Crackles” at the bottom of both lungs, when we listen with a stethoscope (called “rales”)
  • “Pitting Edema” in the feet (“pitting” means when you push in on swollen skin, it leaves an indentation, best checked for over the ankle and shin bones; not just indentations left by socks)
  • Distended (puffed out) neck veins from extra fluid (especially if we push on the liver)
  • Weight gain from extra fluid (changes in body weight is the best way to measure fluid)
  • Certain extra sounds in the heart (called “gallops”), sometime certain heart murmurs.

Tests for HF

The easiest test to confirm HF is the Brain-type Natriuretic Peptide (BNP).  It has nothing to do with the brain itself (just resembles a chemical also found there).  The BNP may be elevated in even mild HF, when physical exam is normal.  Values >400 pg/ml are always positive; if the BNP is <100 pg/ml, HF is most unlikely. Click link for summary of variations on this test that may confuse.

An Echocardiogram (ultrasound of the heart) is even more useful, but takes longer to obtain.  Known as an “Echo,” it can measure how well each side of the heart is pumping, & offer clues to the cause of HF.  If the BNP is elevated, an Echo is certainly part of our work-up.

EKG & Chest X-ray (CXR) are less useful.  They can diagnose severe HF, but may well be normal in mild cases.  We order them nonetheless.  The EKG might detect an old M.I. (a cause of HF), while the CXR can identify other causes of SOB.

There are many causes of HF, including worn out heart muscle from long-standing hypertension; dead muscle from prior M.I.; damaged heart valves; abnormal heart rhythms; compression of heart by fluid surrounding it; kidney failure; various diseases of heart muscle due to viruses, alcohol or toxins, inflammatory conditions (like rheumatoid arthritis), and lots more.  Maybe the heart failure is due to anemia, which is due to colon cancer.  Whenever we diagnose HF, we always ask ourselves, “why?”!

One rare but often overlooked type of HF is Myocarditis, inflammation of the heart muscle.  It’s usually caused by a virus, occurs mostly under age 50, and thus is often misdiagnosed as asthma (SOB and cough) or “the flu” (SOB with fever & muscle aches).  Any time we diagnose “New Onset Asthma” in a youngish person, we should at least think if Myocarditis might be a possibility.  If the patient doesn’t respond to asthma treatment, question the diagnosis.

Clinical findings of acute Myocarditis are similar to those of any cause of heart failure, but clinicians get fooled by the patient’s age.  The CXR will often show a large heart.  The common liver test “AST” may be useful, because a normal result speaks against Myocarditis.

**  Anemia  —  This is a common reason for new-onset SOB.  Anemia means a decrease in red blood cells (RBC’s), which are necessary for circulating oxygen in the bloodstream.  The extent of SOB depends on a combination of how fast RBC’s decline, and how severely. See also Acute Anemia.

We measure RBCs primarily by testing for the amount of hemoglobin (the chemical in RBCs, with iron, that makes our blood red & carries oxygen).  A rapid drop in hemoglobin level from, say, 14 grams to 11 g can be quite symptomatic, while in poor parts of the world, people work hard in the fields, asymptomatic despite their chronic hemoglobins of 9-10 g.  Instead of just ordering a “hemoglobin” test, we almost always order a Complete Blood Count (CBC).

Anemia causes acute SOB in two contexts.  Maybe there’d been slow bleeding which either just reached the point of causing noticeable SOB, or just suddenly got worse.  Alternatively, maybe rapid internal bleeding just began.  In the latter case, the hemoglobin may be relatively normal; see Acute Anemia for an explanation.

We always order a CBC in the work-up of SOB.  Of course, if we find anemia, we have to identify its cause.  We can’t just prescribe iron tablets, because 1) there are a number of types of anemia unrelated to iron levels; and 2) even if a person has iron-deficiency, we’d better figure out why (maybe slow blood loss from a cancer?).  If interested, see our full topic Anemia.

**  Pneumonia  —  This is not a tricky diagnosis when a patient complains of SOB.  There’s usually a cough and fever.  We might hear crackles (“rales”) on stethoscope exam, but the lung may often sound completely normal.

Symptoms may develop within hours, invariably during the first day.  However, some people get a “secondary pneumonia” during Viral Influenza, because the virus affects their immune system.  Anyone who has a flu, starts to get better, & then gets a high fever with new cough & SOB probably has pneumonia.

A Chest X-ray (CXR) is almost 100% able to diagnose bacterial pneumonias, certainly in adults, also in children over five years-old.  I’m very skeptical of “pneumonia” with a normal x-ray.

The temperature can be tricky.  Low-grade fevers also occur with Deep Venous Thrombosis & Pulmonary Embolism, and CXR abnormalities with a PE can mimic pneumonia.  See our discussion in Acute Cough.

**  Anaphylaxis  —  This is an Acute Allergic Reaction.   While not common, it should always be considered in the patient with very new-onset SOB, because there’s life-saving immediate treatment available.  For a patient with a few minutes or hours of sudden, new SOB, diagnose anaphylaxis if EITHER of the following criteria:

Criterion #1:

  • generalized itching, hives, flushing; OR
  • swollen lips, tongue, or uvula (little skin tag we have hanging in middle of throat)

Criterion #2:

  • history of exposure to a likely allergy trigger; PLUS
  • either persistent vomiting/abdominal cramps, or loss of blood pressure

Anaphylaxis usually just causes itchy hives.  But it can cause life-threatening SOB if the throat swells shut, and also fatal Shock (loss of blood pressure).  If the allergy causes bronchospasm, resembling asthma, it’s a little less severe.

Note that these allergic reactions don’t advance from one form to another.  If a person develops hives, then only the skin will be involved.  This time, at least.

Common triggers (the medical term is “allergen”) — medications, bees, nuts, shellfish, maybe any fish (also milk, eggs, soy in children). 

If you think someone is having a life-threatening anaphylactic reaction, call 911 without delay.  (see How to Call 911).  Borrow someone’s EpiPen® if available (Promise to reimburse the maybe-$300. Also, in her CPR class, my daughter was taught never to use someone else’s Epi-Pen — Nonsense!).  The only time it might be dangerous to give the epinephrine (aka adrenalin) is if the person is old enough to be at risk of heart disease (men >40, women >45).

NOTE that up to 25% of allergic reactions occur in two phases.  The person recovers, then relapses within the next 2 days.  So definitely seek immediate medical help for any reaction worse than hives, & be sure the healthcare provider taking care of you has a plan for you in case of relapse.

Errors to avoid [may prove fatal]:

  • Get a reaction in a restaurant, & running to the bathroom
  • Propping up a person who collapses (blood won’t circulate)
  • Using an asthma inhaler instead of an EpiPen®

True story (3rd hand) — A woman got stung by a bee in an elevator, went allergic.  A man there, sensing her distress & not knowing what to do, reached out to touch.  The women, furious at being touched by a strange man, experienced a natural burst of adrenalin (“fight or flight reaction”), & the allergy subsided!  Moral — if someone has a life-threatening allergic reaction, maybe try doing something really outrageous or obscene [though best to explain first to a bystander].

**  Shock (early)  —  Shock usually is easy to diagnose by low blood pressure.  But in the early stages, when it’s just beginning, a person might simply feel new SOB.  Usually there’s an obvious reason why somebody’s in shock, like major trauma, heart attack, allergic reaction.  But the tricky case is an overwhelming infection (Sepsis).  This usually gives a fever…

BUT NOT in the Elderly.  They might have a life-threatening infection, & merely feel SOB.  They’d probably also feel dizzy when they stand up, & might have chills.  By the time they crash and are obviously ill, it may be too late.  “Elderly” is usually defined as over 65 (plenty of healthy people over 65 might object to the label, but their medical providers won’t).

Clinicians can diagnose early Shock by having a person lie down for 5 minutes, take their pulse (heart rate) and blood pressure, then have them stand abruptly and repeat the measurements in 1-2 minutes.  A large rise in pulse or fall in blood pressure clues us in (see Postural Vital Signs).  But the moral is, any time an elderly person feels newly SOB without obvious explanation, we need to take it very seriously.

**  Upper Airway Obstruction  —  These conditions are rare, include Anaphylaxis (see above) and tumors.  The key sign for us is hearing “stridor” with a stethoscope when listening to the lungs (if severe, can be heard without one).  Stridor sounds just like a “wheeze” but occurs during inspiration while breathing in (wheezes are always in expiration, breathing out).  It’s heard  best right over the trachea.

This needs a rapid diagnosis, because it can quickly become life-threatening.  If we think it’s from an allergy, we treat for anaphylaxis (see above).  If not, we send to an ENT Specialist (or even to an ER) for laryngoscopy (looking down the throat & trachea with a laryngoscope).  Stridor plus Fever could be due to very rare life-threatening oral infections (see Sore Throat).

If None of the Above

If we believe a patient has “true” SOB as explained at the beginning, and we decide that none of the above serious conditions seems likely, our best explanation is:

**  Bronchospasm  —  This means that bronchi in the lungs are inflamed and/or constricted (see Diagram — Lower Respiratory Tract).  This can be due to viral lung infection (Influenza & other viruses), Asthma, or an exacerbation of Chronic Obstructive Pulmonary Disease (COPD).

We discuss these conditions in more depth in Acute Cough and Chronic Cough, because cough is always present with an attack of COPD and acute Viral Infection (also called Acute Bronchitis), & virtually always with Asthma.  I’m very reluctant to diagnose either if there isn’t any.  However, on occasions Asthma can cause SOB alone, without a cough.

We diagnose Bronchospasm with our stethoscopes, by hearing wheezes — long high-pitched sounds during expiration.  However, the wheeze may be overshadowed by mostly squeaks and gurgles.  And the key finding above all is a “long expiratory phase” when listening by stethoscope.  If your examiner ever tells you, “the lungs are clear,” ask if expiration sounds longer than inspiration.  If so, it’s Bronchospasm.

If I think a patient has Bronchospasm, I measure how much air they can force out through a small “peak flow meter,” and give them a 10-minute treatment with nebulized albuterol (a medicine that opens the bronchi).  If they feel better afterwards, & their “peak flow” improves, it’s bronchospasm.

A rare error: mistaking “stridor” for a wheeze (see Upper Airway Obstruction above).  It almost never happens, because a) most clinicians easily know the difference; and b) such conditions are very uncommon.

Some asthmatics only get symptoms during exertion, not when they’re sitting in front of us.  In fact, “exercise-induced asthma” may only cause SOB and not necessarily a cough.  So then we prescribe an albuterol inhaler to use before exercise (or also whenever they get symptoms).  If that works, & they no longer get SOB with exertion, we’ve made a diagnosis.

HOWEVER, we never feel so self-confident that this will wind up being the case.  As such, with no certain diagnosis at the end of our first visit, we’d also consider ordering tests to rule out other possibilities in the Table.  As mentioned above, these may include:

Once Again — we should always take the symptom acute SOB seriously, because anything that threatens our oxygen supply can be fatal.  Of course, we determine that the patient’s words “trouble breathing” actually corresponds to what we mean by “True SOB” (best established by confirming that symptoms get worse with exertion).  If not, we’re dealing with “Fatigue,” which has a completely different list of diagnostic possibilities.

See also Acute SOB for the clinician’s condensed thought-process when face-to-face with a patient.

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